1. Field of the Invention
The present invention relates to an adjusting frequency device for oscillator and a method thereof, in particular, the present invention relates to an adjusting frequency device of built-in oscillator for USB interface and a method thereof.
2. Background of the Invention
In conventional devices, such as phase lock loops (PLL) architecture, it is impossible to lock to synchronize the bit-rates of data stream in USB data transmission specification. Since PLL requires longer and continuous input reference clock to accomplish lock operations, it hence needs very long lock time and the circuits designed must be accurate, otherwise it might cause clock errors and erroneously fetched reference signals would probably occur.
In the U.S. Pat. No. 6,407,641, titled as “AUTO-LOCKING OSCILLATOR FOR DATA COMMUNICATION”, there disclosed a technology for solving the above-mentioned problems. Refer to FIG. 1, a block diagram for an automatic adjusting oscillator of prior art is shown, wherein mainly comprising an adjusting circuit 101 and an oscillator 102. The data stream analysis module 104 receives a data stream and a clock signal from an input 112 and an input 116, respectively. The data analysis module sends a control signal C to control a coarse tuning circuit 106, then outputs a control signal F to control a fine tuning circuit 108. Following this, the coarse tuning circuit 106 then sends a control signal C1 to the oscillator 102 to adjust oscillating frequency, whereas the fine tuning circuit 108 sends a control signal F1 to the oscillator 102. Finally, the oscillator 102 outputs and feeds back the well-adjusted frequency.
The technology disclosed in U.S. Pat. No. 6,407,641 though improved the well-known problems; however, during the process of the coarse tuning circuit 106 therein it still requires four-bit input reference data, and during the process of the fine tuning circuit 108 it also requires twenty-bit input reference data, such technology therefore still needs to count long USB packet data from the host transmit side as reference signals. Besides, it is also necessary to incorporate the use of high frequency timings to perform actions of error counting, so as to adjust frequency to reduce the chances that the reference signals being erroneously fetched.